System, particularly an electrohydraulic system, for adjusting the pressure force of a continuously variable transmission

ABSTRACT

A system ( 10 ), in particular an electrohydraulic system ( 10 ), for adjusting the contract pressures of a continuously variable gear, in particular a double-cone pulley belt-contact gear, which has a device for changing the gear ratio of the gear having at least one primary pressure chamber and one secondary pressure chamber is proposed. An electrically triggerable primary pressure valve (V prim ) for adjusting the pressure in the primary pressure chamber and an electrically triggerable secondary pressure valve (V sec ) for adjusting the pressure in the secondary pressure chamber are provided. The pressure (p prim ) of the primary pressure chamber and the pressure (p sec ) of the secondary pressure chamber can be carried to the secondary pressure valve (V sec ). The object is to enable a more-accurate adjustment of the pressure (p prim ) in the primary pressure chamber. To that end, the trigger current (I sec ) of the secondary valve (V sec ) is set to a value which corresponds to a predetermined pressure (p sec,soll ) in the primary and the secondary pressure chamber. Moreover, the pressure (p sec,soll ) in the secondary pressure chamber is regulated, via the trigger current (I prim ) of the primary valve (V prim ), so that the pressure (p prim ) in the primary pressure chamber is established indirectly.

PRIOR ART

[0001] The invention is based on a system, in particular an electrohydraulic system, for adjusting the contract pressures of a continuously variable gear, as generically defined by the preamble to the main claim.

[0002] One such system is known from German Patent Disclosure DE 195 19 162 A1, for example, or U.S. Pat. No. 5,971,876. A device for changing the ratio of the gear, having a primary pressure chamber and a secondary pressure chamber, is provided. Moreover, an electrically triggerable primary pressure valve for adjusting the pressure in the primary pressure chamber and an electrically triggerable secondary pressure valve for adjusting the pressure in the secondary pressure chamber are present. The pressure of the primary pressure chamber and the pressure of the secondary pressure chamber can be carried to the secondary pressure valve.

[0003] In such a gear, the contract pressures must be adjusted such that no slip of a belt contact means occurs. However, care also be taken to assure that the contract pressures and hence wear not become unnecessarily great. Particularly when the gear is at a standstill, the possibility exists that the contract pressure, generated in the secondary pressure chamber, of the secondary pulley will not be transmitted fully to the primary pulley. An accurate adjustment of the pressure in the primary pressure chamber and of the contract pressure thus generated of the primary pulley is therefore necessary. An accurate adjustment of the pressure in the primary pressure chamber is possible only with difficulty.

ADVANTAGES OF THE INVENTION

[0004] The system according to the invention for adjusting the contract pressures of a continuously variable gear, having the definitive characteristics of the main claim, has the advantage over the prior art that a more-accurate adjustment of the pressure in the primary pressure chamber is possible. This is true particularly when the gear is at a standstill. It is also advantageous to do so when the gear is virtually at a standstill or is at the maximum gear ratio.

[0005] Further advantages and advantageous refinements of the system of the invention for adjusting the contract pressures of a continuously variable gear will become apparent from the dependent claims and the description.

DRAWING

[0006] One exemplary embodiment of the invention is shown in the drawing and explained in further detail in the ensuing description.

[0007] In FIG. 1, a detail of a hydraulic circuit diagram is shown, and

[0008] in FIG. 2, there is a graph which illustrates the relationship between pressures and currents.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0009] In FIG. 1, a system 10 for adjusting the contract pressures of a continuously variable gear, not shown, in particular a double-cone pulley belt-contact gear, is shown. This system and its mode of operation are known for example from DE 195 19 162 A1 or U.S. Pat. No. 5,971,876.

[0010] A device, also not shown, for changing the ratio of the gear is also present and has at least one primary pressure chamber and one secondary pressure chamber. The system 10 communicates with the primary pressure chamber via a line 12 and with the secondary pressure chamber via a line 14. An electrically triggerable primary pressure valve V_(prim) for adjusting the pressure p_(prim) in the primary pressure chamber and an electrically triggerable secondary pressure valve V_(sec) for adjusting the pressure p_(sec) in the secondary pressure chamber are provided. From the line 14, a line 18 leads to the primary valve V_(prim), from where the aforementioned line 14 leads to the primary pressure chamber. The pressure p_(prim) is carried via a control line 16 to a pressure face of the secondary pressure valve V_(sec), and as can be seen from FIG. 1, it acts counter to the force generated by the electrical triggering. The control line 16 can also be switchable via an additional valve—not shown. The pressure p_(sec) is carried via a control line 20 to a different pressure face of the secondary pressure valve V_(sec).

[0011] In operation of the gear, particularly when it is at a standstill, the requisite pressure p_(pri,soll) in the primary pressure chamber and the requisite pressure p_(sec,soll) in the secondary pressure chamber can be determined via a performance graph, as known for example from DE 195 19 162 A1 or U.S. Pat. No. 5,971,876.

[0012] Moreover, for more-accurate adjustment of the pressure p_(prim) in the primary pressure chamber, the trigger current I_(sec), of the secondary valve V_(sec) is set to a required value I_(sec,soll), which corresponds to a predetermined pressure p_(pri,soll) in the primary pressure chamber and to a predetermined pressure p_(sec,soll) in the secondary pressure chamber. The pressure p_(sec) in the secondary pressure chamber is moreover regulated via the trigger current I_(prim) of the primary valve V_(prim), so that the pressure p_(prim) in the primary pressure chamber is established indirectly. The trigger currents I_(prim) and I_(sec) correspond to control signals for the valves V_(prim) and V_(sec). If the valves V_(prim) and V_(sec) are not electrically triggered but are instead triggered hydraulically, then the control signals instead correspond to their pressures. However, regulation via electrical control signals in the form of trigger currents is more suitable.

[0013] For further improved control of the pressure p_(prim) in the primary pressure chamber, the trigger current I_(sec) of the secondary valve V_(sec) is defined, in accordance with the formula

f(I _(sec))=k _(prim) *p _(pri,soll) +k _(sec) *p _(sec,soll)

[0014] as a function of the sum of the product of a constant k_(prim) of the primary pressure valve V_(prim) and the pressure p_(prim,soll) of the primary pressure chamber, and the product of a constant k_(sec) of the secondary pressure valve V_(sec) and the pressure p_(sec,soll) of the secondary pressure chamber, which is done by regulating the pressure p_(sec) in the secondary pressure chamber. The constant k_(prim) and k_(sec) depend on various factors, such as the effective surface areas of the valves V_(prim), i V_(sec) to which the pressures p_(prim), p_(sec) are applied.

[0015] The regulation of the pressure p_(prim) in the primary pressure chamber can also be improved further by providing that the pressure p_(sec) in the secondary pressure chamber is regulated using the trigger current I_(prim) of the primary pressure valve. This is a reversal of the triggering of pressure chambers compared to normal operation, and it is especially advantageous when the gear is at a standstill. It is also advantageous if the adjustment of the contract pressures is done when the gear is virtually at a standstill and/or is at the maximum gear ratio.

[0016] To that end, preferably the required and measured pressures p_(sec,soll) and p_(sec) in the secondary pressure chamber are delivered to a controller, such as a PID controller, whose outcome is used to determine the trigger current I_(prim) of the primary pressure valve.

[0017] The regulating means, for example in the form of a controller with a suitable program, can contain an adaptation algorithm, with which the relationship between the predetermined pressure in the primary pressure chamber p_(pri,soll) and the predetermined pressure in the secondary pressure chamber p_(sec,soll) is learned in ongoing operation using the control signal, that is, the trigger current I_(sec) of the secondary valve. This can preferably be done in a mode of operation in which the primary pressure p_(prim) is nearly equal to the secondary pressure p_(sec), or in which the primary pressure p_(prim) is zero. For establishing the operating state in which the pressure (p_(prim)) in the primary pressure chamber is approximately equal to the pressure (p_(sec)) in the secondary pressure chamber, the primary pressure valve (V_(sec)) is opened in the direction of secondary pressure with the aid of the control signal (I_(prim)). For establishing the operating state in which the pressure (p_(prim)) in the primary pressure chamber is zero, the primary pressure valve (V_(sec)) is opened in the direction of low pressure with the aid of the control signal (I_(prim)).

[0018] In an advantageous feature, precisely one offset value or offset control signal I_(sec,offset) of the control signal I_(sec) is adapted, at which a predetermined pressure p_(pri,soll) in the primary pressure chamber and a predetermined pressure p_(sec,soll) in the secondary pressure chamber are established. The adaptation is effected by comparison of the predetermined pressure p_(sec,soll) in the secondary pressure chamber with the measured pressure p_(sec) in the secondary pressure chamber. That is, the ascertainment of the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber, the measured secondary pressure (p_(sec)) is compared with a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber. As a function of the comparison, the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is corrected. As a result, the requisite control signal I_(sec) can be adapted constantly, or in other words can be adapted to the ideal value at a given time for establishing the pressure p_(prim) in the primary pressure chamber. This is more flexible, compared to using a single fixed value, for instance from a defined performance graph. This makes the establishment of the pressure p_(prim) more accurate.

[0019]FIG. 2 shows a graph illustrating the relationship between the currents I_(prim) and I_(sec) and the pressures p_(rim) and p_(sec) more clearly; it is also more readily apparent from this how the pressure p_(sec) in the secondary pressure chamber is regulated via the control signal I_(prim) of the primary valve V_(prim), and how the pressure p_(prim) in the primary pressure chamber is established indirectly in the process. What is important here above all is the pressure ratio, generated by the control lines 16 and 20, at the secondary pressure valve V_(sec).

[0020] Via the control line 20, which returns the pressure p_(sec) to the secondary pressure valve V_(sec), it is unambiguously defined what the pressure ratios are, since a force generated via the electrical triggering acts counter to the contrary force generated by the returned pressure. This is not true for the primary pressure valve V_(prim), since the pressure p_(prim) is not returned to the primary pressure valve V_(prim).

[0021] From the graph, it can be seen that when the primary pressure valve V_(prim) conducts the pressure out of the primary pressure chamber into the tank, the pressure p_(sec) takes the course represented by the line p_(prim)=0, until the maximum generatable pressure for p_(sec) is reached. Based on this, via the current I_(prim), the pressure p_(prim) can be adjusted to the value p_(pri,soll). This is illustrated by the double arrows in FIG. 2. The line is shifted parallel, until the desired pressure p_(prim)=p_(pri,soll) is reached.

[0022] In operation, the requisite pressure p_(sec,soll) in the secondary pressure chamber is now, as already mentioned, determined via a performance graph—for instance as known from DE 195 19 162 A1 or U.S. Pat. No. 5,971,876. The current I_(sec) is then set to the value I_(sec,soll) required for this purpose, and is left there. Next, via the current I_(prim), the primary pressure valve V_(prim) is actuated, as a result of which the pressure p_(prim) also changes. The pressure p_(prim) is carried via the control line 20 to the secondary pressure valve V_(sec). As a result, the secondary pressure valve V_(sec) adjusts. The pressure p_(sec) thus changes, which in turn affects the pressure p_(prim). As a consequence, the pressure p_(prim) is established indirectly. Thus via the current I_(prim), the pressure p_(sec) in the secondary pressure chamber is regulated, and the pressure p_(prim) in the primary pressure chamber is established indirectly. 

1. A system (10), in particular an electrohydraulic system (10), for adjusting the contract pressures of a continuously variable gear, in particular a double-cone pulley belt-contact gear, which has a device for changing the gear ratio of the gear having at least one primary pressure chamber and one secondary pressure chamber, having an electrically triggerable primary pressure valve (V_(prim)) for adjusting the pressure in the primary pressure chamber and an electrically triggerable secondary pressure valve (V_(sec)) for adjusting the pressure in the secondary pressure chamber, the pressure (p_(prim)) of the primary pressure chamber and the pressure (p_(sec)) of the secondary pressure chamber being carried to the secondary pressure valve (V_(sec)), characterized in that the control signal (I_(sec)) of the secondary valve (V_(sec)) is set to a value (I_(sec,soll)) which corresponds to a predetermined pressure (p_(prim,soll)) in the primary pressure chamber and to a predetermined pressure (p_(sec,soll)) in the secondary pressure chamber, and the pressure (p_(sec)) in the secondary pressure chamber is regulated via the control signal (I_(prim)) of the primary valve (V_(prim)), so that the pressure (p_(prim)) in the primary pressure chamber is established indirectly.
 2. The system (10) of claim 1, characterized in that for controlling the pressure (p_(prim)) in the primary pressure chamber, the control signal (I_(sec)) of the secondary valve (V_(sec)) is defined as a function of the sum of the product of a constant (k_(prim)) of the primary pressure valve (V_(sec)) and the pressure (p_(prim,soll)) of the primary pressure chamber, and the product of a constant (k_(sec)) of the secondary pressure valve (V_(sec)) and the pressure (p_(sec,soll)) of the secondary pressure chamber, which is done by regulating the pressure (p_(sec)) in the secondary pressure chamber.
 3. The system (10) of claim 1 or 2, characterized in that the pressure (p_(sec)) in the secondary pressure chamber is regulated with the control signal (I_(sec)) of the primary pressure valve (V_(prim)).
 4. The system (10) of one of claims 1-3, characterized in that the requisite pressure (p_(soll)) and the measured pressure (p_(ist)) in the secondary pressure chamber are delivered to a controller, whose outcome is used to determine the control signal (I_(prim)) of the primary pressure valve (V_(prim)).
 5. The system (10) of one of claims 1-4, characterized in that the adjustment of the contract pressures is done when the gear is at a standstill.
 6. The system (10) of one of claims 1-5, characterized in that for adjusting the pressure (p_(sec)) in the secondary pressure chamber to the predetermined pressure (p_(sec,soll)), a PID controller is used in the secondary pressure chamber.
 7. The system (10) of one of claims 1-6, characterized in that means are provided with which the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is varied during operation on the order of an adaptation.
 8. The system (10) of claim 7, characterized in that the ascertainment of the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is effected in an operating state in which the pressure (p_(prim)) in the primary pressure chamber is zero.
 9. The system (10) of claim 8, characterized in that for establishing the operating state in which the pressure (p_(prim)) in the primary pressure chamber is zero, the primary pressure valve (V_(sec)) is opened in the direction of low pressure with the aid of the control signal (I_(prim)).
 10. The system (10) of claim 7, characterized in that the ascertainment of the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is effected in an operating state in which the pressure (p_(prim)) in the primary pressure chamber is approximately equal to the pressure (p_(sec)) in the secondary pressure chamber.
 11. The system (10) of claim 10, characterized in that for establishing the operating state in which the pressure (p_(prim)) in the primary pressure chamber is approximately equal to the pressure (p_(sec)) in the secondary pressure chamber, the primary pressure valve (V_(sec)) is opened in the direction of secondary pressure with the aid of the control signal (I_(prim)).
 12. The system (10) of one of claims 7-11, characterized in that the ascertainment of the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is effected in the form of determining an offset control signal (I_(sec,offset)).
 13. The system (10) of one of claims 7-12, characterized in that the ascertainment of the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber, the measured secondary pressure (p_(sec)) is compared with a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber, and as a function of the comparison, the relationship between the control signal (I_(sec)) of the secondary valve (V_(sec)) and the predetermined pressure (p_(prim,soll)) in the primary pressure chamber and a predetermined pressure (p_(sec,soll)) of the secondary pressure chamber is corrected.
 14. The system (10) of one of claims 1-13, characterized in that the adjustment of the contract pressures is effected when the gear is virtually at a standstill and/or is at the highest gear ratio. 